The correct way to use your own NSError objects in your app

	// A function that returns an object or nil if there's an error.
	- (NSObject*) doSomethingComplexAndReturnObject:(NSString*) input error:(NSError**) error {
	// do some work..
	BOOL itWorked = YES;
	if (itWorked) {
	return [[NSObject alloc] init]; // Do better memory management than this please.
	} else {
	*error = [NSError errorWithDomain:@"com.mycompany.myapp" code:14 userInfo:[NSDictionary dictionaryWithObject:@"My error message" forKey:NSLocalizedDescriptionKey]];
	return nil;
	}
	}
	// This function demonstrates using the function above
	- (void) useTheDoSomethingComplexFunction {
	NSError* error = nil;
	NSObject* ob = [self doSomethingComplexAndReturnObject:@"foobar" error:&error];
	if (ob) {
	// do the success thing!
	} else if (error) {
	NSLog(@"Can't do the success thing as we have an error %@", [error localizedDescription] );
	}
	}

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Thanks to Mike Abdullah @mikeabdullah for pointing out the 'deliberate' (ahem) mistake in this post the first time around. Oops.